Expander Demonstrator

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Jérôme Breteau & Jean-Noël Caruana Future Launcher Preparatory Programme, Directorate of Launchers, ESA HQ, Paris, France

he technical difficulties encountered by other spacefaring countries in similar T ‘expander-cycle’ engine projects show how demanding it is to master this kind of technology. So the achievements of ESA’s Future Launchers Preparatory Programme (FLPP) Expander Demonstrator Project, including several European ‘firsts’, are essential contributions to the development of future cryogenic upper-stage engines.

Introduction In launch vehicles, one of the key enabling technologies is the propulsion system, but this is complicated to acquire and takes a long time in development. This is especially true for upper-stage engines, where use of cryogenic propellants such as liquid hydrogen and oxygen and reignition capability are essential in order to reach high-energy orbits with heavy payloads. Upper-stage engines also operate in specific conditions (vacuum, microgravity) that are difficult to reproduce on Earth, and involve significant development risks that have to be mitigated.

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Expander Demonstrator

Jérôme Breteau & Jean-Noël Caruana Future Launcher Preparatory Programme, Directorate of Launchers, ESA HQ, Paris, France

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Launchers Expander Demonstrator

In 1998 ESA, CNES and Arianespace project called the ‘Cryogenic Reignitable (TRL) of the engine and its decided to develop an enhanced Upper Stage Engine – Expander components, currently estimated cryogenic upper-stage for the Ariane-5 Demonstrator’. between 3 and 5, depending on the launcher in order to respond to the subjects under study, must be raised to rapid evolution of the global Project Objectives level 6 (prototype test in a relevant commercial market towards more heavy The main aim of the FLPP Expander environment), in order to properly assess payloads. In recognition of the quick Demonstrator Project is to supply the risks, cost and duration of a further emergence of this new commercial need elements allowing a sound, informed development phase up to qualification and the comparatively long decision about the next steps in the (TRL 8). The definition of T development time of a propulsion development of the cryogenic reignit- Most engine components have already system, it was decided to select a two- able upper-stage engine. More precisely, reached a TRL of 5 and are close to step approach to increase Ariane-5’s in- the implementation of this objective achieving the target of TRL 6. The most the opera ydrogen environments, (including reliability, projected mass and orbit delivery capability. requires detailed studies of the engine’s significant issues to process are linked to propellant mixtur egarding ‘embrittlement’ performance, production cost, develop- The first step was the development of operating domain and assessment of its component life duration and per- feeding conditions); ment duration and cost). an adaptation of the existing Ariane-4 design through extensive, full-scale formance assessment or behaviour in – nominal perfor xperience for the engine. This exercise is initiated at an early H10 propulsion system for a new upper- engine testing in hot-firing conditions. operational conditions (pollution, exploration of stage of the launcher design because stage called ESC-A. The second step This will make it possible to increase transient conditions, etc.). The Tech- (thrust, mixture ra the FLPP Expander experience and theory show that an involved the development of an our knowledge and understanding of nological Readiness Levels of some turbopumps); oject is to overcome the overall optimised design is not necessarily adaptation of this stage to create the expander-cycle engine operations and innovative components, like the Nozzle – characterisation of ed in the assembly of optimised subsystems. ESC-B version with a new cryogenic technologies, yielding propulsion data Extension Deployment system or the stability of epare The highest performance engine, optimal engine, the ‘Vinci’. The initial ESC-B for launcher system optimisation, in igniter, are lower compared to other conditions; ble at a further stage. from a propulsion point of view, might flight was planned in 2006, following on addition to the proper development and engine technologies and require – first experience f not be the best global solution due to from the introduction of ESC-A. safeguarding of the relevant European dedicated subsystem technology tests if integrat ade-off at stage and specifications and constraints at a higher However, although Ariane-5 ECA competencies in cryogenic propulsion. It they are to be improved. system level. There is a continuous entered operational service, a should be noted that the development of There are many more significant – ated exchange of data between the engine and combination of factors including a the Vinci engine, before it was inter- technological steps in the FLPP d the launcher system throughout the downturn in the commercial market rupted, had just reached a stage that Expander Demonstrator Project that entire preliminary design process, starting delayed and then stopped the allowed the Expander Demonstrator contribute to the improvement of the – or with high-level performance data, such as development of the ESC-B stage and the Project to gain direct experience at the engine TRL. These are: the following: Vinci engine. engine hot-firing test level. – definition of an optimised starting . – thrust level; At the same time, launch system and shutdown sequence with respect – mixture ratio; studies within FLPP showed clearly the Assessment of operating domain and to progressivity, duration and – – specific impulse; need for a versatile, high-performance, design maturation propellant consumption; – restart capability; evolved cryogenic upper-stage engine The Technological Readiness Level – verification of engine stability over the – thrust-to-weight ratio; capable of delivering payloads to all – – physical interfaces; kinds of orbits, ranging from Low Earth Orbit up to exploration missions in deep Expander closed-cycle engine: how does it work? space. A high-performance upper-stage The expander thermodynamic cycle is a ‘closed cycle’, meaning that the propellants flow together engine appeared to be a central element through the thrust chamber, hence maximising the for the future launcher scenarios of the specific impulse, an indicator of engine FLPP, and a cryogenic expander engine performance. The combustion chamber pressure offered high expectations in terms of is higher than the tank pressure (~60 bars performance and reliability. compared to 2–5 bars). This pressure rise is It became quickly obvious that the ensured via two centrifugal turbopumps driven by availability of a set of expander-cycle turbines installed on the pump shafts. upper-stage engines offered a unique opportunity to progress in the The turbines are activated by the flow of high- preparation of upper-stage engines for pressure gaseous hydrogen obtained by all future launcher configurations. circulating the hydrogen pump discharge flow It was, therefore, decided at the end of around the hot combustion chamber walls. After 2005 to transfer the management and being heated up in the combustion chamber jacket, the hydrogen flows existing assets of the former Vinci through the turbines and is injected into the combustion chamber. Then, mixed with the liquid oxygen flow, it combusts and produces the hot-gas flow development to the FLPP in order to that provides the rocket engine’s thrust. form the basis of a demonstration

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Launchers Expander Demonstrator

In 1998 ESA, CNES and Arianespace project called the ‘Cryogenic Reignitable (TRL) of the engine and its decided to develop an enhanced Upper Stage Engine – Expander components, currently estimated cryogenic upper-stage for the Ariane-5 Demonstrator’. between 3 and 5, depending on the launcher in order to respond to the subjects under study, must be raised to rapid evolution of the global Project Objectives level 6 (prototype test in a relevant commercial market towards more heavy The main aim of the FLPP Expander environment), in order to properly assess payloads. In recognition of the quick Demonstrator Project is to supply the risks, cost and duration of a further emergence of this new commercial need elements allowing a sound, informed development phase up to qualification and the comparatively long decision about the next steps in the (TRL 8). The definition of Technology Readiness Levels used by ESA, NASA and many other agencies and companies worldwide development time of a propulsion development of the cryogenic reignit- Most engine components have already system, it was decided to select a two- able upper-stage engine. More precisely, reached a TRL of 5 and are close to step approach to increase Ariane-5’s in- the implementation of this objective achieving the target of TRL 6. The most the operating domain (thrust level, gaseous hydrogen environments, (including reliability, projected mass and orbit delivery capability. requires detailed studies of the engine’s significant issues to process are linked to propellant mixture ratio, propellant especially regarding ‘embrittlement’ performance, production cost, develop- The first step was the development of operating domain and assessment of its component life duration and per- feeding conditions); and tightness; and ment duration and cost). an adaptation of the existing Ariane-4 design through extensive, full-scale formance assessment or behaviour in – nominal performance of the engine, – reignition experience for the engine. This exercise is initiated at an early H10 propulsion system for a new upper- engine testing in hot-firing conditions. operational conditions (pollution, exploration of the operating domain stage of the launcher design because stage called ESC-A. The second step This will make it possible to increase transient conditions, etc.). The Tech- (thrust, mixture ratio, regimes of One task of the FLPP Expander experience and theory show that an involved the development of an our knowledge and understanding of nological Readiness Levels of some turbopumps); Demonstrator Project is to overcome the overall optimised design is not necessarily adaptation of this stage to create the expander-cycle engine operations and innovative components, like the Nozzle – characterisation of the accuracy and contingencies encountered in the assembly of optimised subsystems. ESC-B version with a new cryogenic technologies, yielding propulsion data Extension Deployment system or the stability of engine operating production or testing, and to prepare The highest performance engine, optimal engine, the ‘Vinci’. The initial ESC-B for launcher system optimisation, in igniter, are lower compared to other conditions; solutions applicable at a further stage. from a propulsion point of view, might flight was planned in 2006, following on addition to the proper development and engine technologies and require – first experience for endurance of not be the best global solution due to from the introduction of ESC-A. safeguarding of the relevant European dedicated subsystem technology tests if integrated technologies in the Data supply for trade-off at stage and specifications and constraints at a higher However, although Ariane-5 ECA competencies in cryogenic propulsion. It they are to be improved. operating domain; system levels system level. There is a continuous entered operational service, a should be noted that the development of There are many more significant – characterisation of the mechanical Propulsion systems are highly integrated exchange of data between the engine and combination of factors including a the Vinci engine, before it was inter- technological steps in the FLPP dynamic behaviour of the complete with the design of rocket stages and the the launcher system throughout the downturn in the commercial market rupted, had just reached a stage that Expander Demonstrator Project that engine; overall launcher system. Preliminary entire preliminary design process, starting delayed and then stopped the allowed the Expander Demonstrator contribute to the improvement of the – assessment of mechanical and launcher system optimisations for with high-level performance data, such as development of the ESC-B stage and the Project to gain direct experience at the engine TRL. These are: thermal loads sustained by the engine potential development are performed in the following: Vinci engine. engine hot-firing test level. – definition of an optimised starting during operation and between boost parallel during the demonstration phase. – thrust level; At the same time, launch system and shutdown sequence with respect phases; They rely upon the FLPP elements and – mixture ratio; studies within FLPP showed clearly the Assessment of operating domain and to progressivity, duration and – chill-down and thermal control studies related to important system – specific impulse; need for a versatile, high-performance, design maturation propellant consumption; optimisation, in view of reignition parameters, such as the impact of – restart capability; evolved cryogenic upper-stage engine The Technological Readiness Level – verification of engine stability over capability; multiboost missions, or elements of the – thrust-to-weight ratio; capable of delivering payloads to all – mastering of high-pressure and warm propulsion system design criteria – physical interfaces; kinds of orbits, ranging from Low Earth Orbit up to exploration missions in deep Expander closed-cycle engine: how does it work? The expander thermodynamic cycle is a ‘closed space. A high-performance upper-stage Expander Demonstrator integration (SNECMA Moteurs) cycle’, meaning that the propellants flow together engine appeared to be a central element through the thrust chamber, hence maximising the for the future launcher scenarios of the specific impulse, an indicator of engine FLPP, and a cryogenic expander engine performance. The combustion chamber pressure offered high expectations in terms of is higher than the tank pressure (~60 bars performance and reliability. compared to 2–5 bars). This pressure rise is It became quickly obvious that the ensured via two centrifugal turbopumps driven by availability of a set of expander-cycle turbines installed on the pump shafts. upper-stage engines offered a unique opportunity to progress in the The turbines are activated by the flow of high- preparation of upper-stage engines for pressure gaseous hydrogen obtained by all future launcher configurations. circulating the hydrogen pump discharge flow It was, therefore, decided at the end of around the hot combustion chamber walls. After 2005 to transfer the management and being heated up in the combustion chamber jacket, the hydrogen flows existing assets of the former Vinci through the turbines and is injected into the combustion chamber. Then, mixed with the liquid oxygen flow, it combusts and produces the hot-gas flow development to the FLPP in order to that provides the rocket engine’s thrust. form the basis of a demonstration

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Launchers Expander Demonstrator

Industrial Organisation Under the leadership of SNECMA Prime, which is responsible for project management, planning, quality, costing and control, as well as propulsion system engineering, a set of sub- contractors from a wide range of European countries is involved in the FLPP Expander Demonstrator Project, representing the highest competence in cryogenic propulsion. This organisation, in place and operational, ensures a low level of project risk in the execution of the activity. The project is supported by 11 ESA Member States (Austria, Belgium, France, Germany, Ireland, Italy, Norway, Spain, Sweden, Switzerland and The Netherlands) and ensures a large and efficient industrial organisation.

The Achievements: European ‘Firsts’ The FLPP Expander Demonstrator Project is structured into various evaluation testing and simulation – pump inlet propellant conditions and maintain a high level of motivation efforts. It encompasses engine tests as constraints; through advanced demonstration well as subsystem tests, with both levels – dynamic environment; projects that employ cryogenic of testing complementing one another. – lifetime/burn duration. propulsion specialists and maintain a Tests at engine level are best suited to buffer of highly skilled engineers able reveal performance limitations or The DLR P4.1 test bench in Lampoldshausen, Germany These contribute towards the supply to solve any difficult technical issues for unforeseen interactions between sub- and maintenance of complete pro- the benefit of the entire launcher systems. Tests at subsystem level pulsion mechanical, thermal or thermo- activity. In this respect, FLPP is one of (combustion chamber, turbopumps, a cumulated firing time exceeding 4000 half the output of a nuclear power reservoir to cool down and condense the dynamic validated models. the major contributors for safeguarding etc.) are more focused on fine seconds. The fifth test campaign is plant. This necessitates the use of several engine exhaust gases. During the tests cryogenic liquid propulsion com- functional characterisation, technology ongoing, and the overall activity is high mass flow steam generators to more than 450 engine parameters are Safeguarding European Competencies petence in Europe. demon-stration, further software tool progressing normally. However, signi- operate the vacuum ejectors, plus a huge recorded and monitored to ensure safe The cryogenic propulsion technologies validation and investigation of ficant tests remain to be logged to reach condenser and underground water testing conditions. currently used for commercial launchers shortcomings. the typical qualification values for this require highly skilled engineers and An expander demonstrator engine running in a hot-firing test, Out of a total of four, two test kind of engine of approximately 60 000 technicians in a wide range of early 2008 (ESA/DLR/SNECMA) campaigns have been performed up to seconds of operating time during 180 specialities. These competences are now in the FLPP and they have already tests. Engine Global Testing specific to space transportation yielded notable results, namely, the first Full-scale hot-firing tests are certainly – 35 engine tests propulsion and are only obtained after reignition in Europe of a cryogenic the most complex ground testing – 10 tests to adjust engine chill-down several years of practice and experience engine, the demonstration of the viability activities in the launcher sector, – 6 tests with partial start-up in these domains. In addition, some of the high-pressure expander-cycle comparable to in-flight tests. The – 19 tests with complete start-up, 6 of them with reignition specific liquid-propulsion competences design, with massive power extraction complete test sequence necessitates the – Validation of closed-loop control in system engineering can be from the combustion chamber, as well as mastering not only of the tested – 3 tests with a composite nozzle cone safeguarded only through the operation the operation of a large-scale and long- equipment but also of the test bench. of complex integrated demonstrators. duration vacuum test cell. The P4.1 vacuum test bench is unique in This is a significant investment for More specifically, four test campaigns Europe. It allows near-vacuum (a few Europe’s future and represents a have been completed under vacuum mbars) ignition and steady state tests of strategic asset for operational launcher conditions at the DLR P4.1 test cryogenic engines of several tens of tons services. It is, therefore, important to bench in Lampoldshausen (Germany), of thrust, representing power dissi- 4110 seconds cumulated firing time with 5 engines safeguard these competencies and totalling 35 tests with six reignitions and pation exceeding 420 MW, equivalent to

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as well as the duration. In addition, the achievements of the demonstration the limited quantity of hardware phase and did not identify any fosters the fulfilment of the expander ‘showstoppers’ for the continuation of demonstration objective of design the activities. maturation by forcing the intensive use of the few available units. The Activities in 2008 testing of five engines has already For 2008, the contracted FLPP Expander revealed some marginal aspects of the Demonstrator activities ensure contin- design, and, as FLPP is still at an early uity in the P4.1 test campaign with the stage of this engine’s hot-fire testing, hot-firing test of two complete engines. may reveal more in the future. This third year of FLPP activity will Difficulties encountered in the course permit further exploration of the of testing and manufacturing are the engines’ capabilities and the first object of roadmaps to find solutions if validation of focused design improve- Subscale combustion chamber (Astrium GmbH) they are serious enough to challenge ments. the major goals of the Demonstrator A complete engine dynamic test Project. campaign will also make it possible to The Expander Demonstrator Project finely characterise the engine behaviour Conclusion also fosters focussed engineering in and validate the mechanical model, The Expander Demonstrator Project is order to prepare the integration with a representing an important milestone now well advanced, resulting in many cryogenic reignitable upper-stage for towards future launcher applications. useful elements for possible improve- View inside P4.1 Test Bench with Expander Demonstrator (DLR /SNECMA Moteurs) several potential launcher applications. Using the same approach, the effect of ments of existing launchers and new The baselines of these engineering microgravity on engine operation will be developments for future launchers. The activities are the functional, thermal Expander Demonstrator mechanical test configuration (SNECMA introduced in the modelling and its maturation of the design and the The test sequence starts with the test This significant amount of testing and mechanical models that are to be Moteurs) impact will be checked. The year 2008 assessment of the engine capabilities have cell emptying to reach near vacuum experience at engine level is required in further improved with regard to physical will also feature subsystem testing, such made significant progress and showed the conditions. Then, prior to ignition, the order to investigate the chill down suitability, prediction ability, and as full-scale combustion chamber tests technical viability of the expander cycle engine is chilled to cryogenic propellant sequence, adjust the ignition criteria interconnectivity or versatility. In this preliminary design, design justification to be performed at the DLR P3.2 test concept. temperatures (i.e. –250°C for liquid and transient sequences, and assess way, they will be a more valuable or test analysis. bench, or similar subscale tests at It is important to highlight the hydrogen and –180°C for liquid oxygen) the thrust and mixture ratio limitations, asset for engine trade-off analysis, The expander cycle and the reignition the P8 Research test bench, both at technical achievements that, for the first in order to avoid thermal shocks during function are the major uncharted fields Lampoldshausen. time in Europe, have been delivered in a the very short start-up sequence. When of the demonstration. Priority in the At subsystem level, several upgrade relatively short timeframe, namely all the desired conditions for ignition are A schematic showing elements of the P4.1 Test Bench engineering effort is being given to studies will be continued, with eventual sustained closed-cycle operation, high- achieved, the start-up sequence is increasing and consolidating the prototype manufacture. At the same pressure expander-cycle operation and initiated through a precise sequencing of models’ Technology Readiness Level in time, subsystem tests, such as water cryogenic engine reignition. the opening and closure of the engine these areas. Significant progress has testing of a liquid oxygen turbopump in In Europe, the FLPP Expander valves and igniter activation. This been made on thermal, mechanical and diphasic conditions, or testing of Demonstrator Project contributes ensures that the turbomachinery is safely functional system models in steady state components such as bearings, are significantly to the safeguarding of the started, followed by ignition of the and transient phases. For example, the planned to investigate operations in off- corresponding competences. During the propellant in the combustion chamber. constant use of transient system design conditions and to validate limited last two years of the FLPP Expander The nominal steady state is then reached simulation was one of the major factors definition upgrades. Demonstrator activities, several of the in less than two seconds, with a total test contributing to the success of the first In a classical approach, the complete lessons learned have been capitalised duration of several hundreds of seconds. engine tests, by limiting the number of batch of simulations is performed in upon, whether in terms of operation of Different operating conditions can be tests needed to establish reliable start parallel in order to achieve the a complex integrated engine test bench tested, thanks to proportional bypass and shutdown sequences, as well as by validation, accuracy, prediction, and such as P4.1 or in terms of expander- valves equipped with electric actuators avoiding any major functional problems data supply objectives of the Project, as cycle specificity. in the engine. At the end of the test, the during the tests. well as to support the corresponding test As a common foundation for several engine is shutdown in a controlled way The year 2007 ended with an campaigns. future launcher configurations, the and purged of remaining propellant to exhaustive review of the technical status A second technical status and results FLPP Expander Demonstrator will start the simulation of the stage ballistic and results of the Expander review is foreseen at the end of 2008 to continue to yield technology achieve- coast phase. Then reignition in vacuum Demonstrator Project, with the monitor the progress of the activities, ments and advancements in the years to is activated, repeating the first test participation of more than sixteen contribute to risk mitigation and come, and will enable efficient transi- sequence, for a second boost before test experts from the entire European provide independent technical analysis tions towards development applications termination. propulsion community, who recognised of any issues encountered. as well as innovative perspectives. e

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